Brian DePalma's "Sisters" was promoted as a routine shocker by its distributor, American International Pictures, back in 1973--the kind of picture that made the studio rich and infamous. But it was something more--and more interesting--than that. It was an homage by a gifted young director to one of the cinema's genuine masters, Alfred Hitchcock.

The theme was very Hitchcockian: a demonstration of the way private sexual obsession has a way of spilling over into public, with murderous consequences {"Vertigo"). There are innocent bystanders drawn dangerously drawn dangerously into a closely woven criminal web ("The Man Who Knew Too Much") and the investigative reporter keeping a sharp eye on the situation next door ("Rear Window"). Even the film's central violent incident reminds us of the most famous scene in "Psycho", as does a splendid, spooky score by that film's masterful composer, Bernard Herrmann. More important than these specific references to glories past, however, is the Hitchcockian discipline De Palma brings to his storytelling, the delicate balance between humor and horror which he permits it to unfold, the suspenseful way he lets the audience in on the plot's secret before his characters tumble into it.

It is a weirdly plausible and marvelously original plot. So are the parodies that enliven the film: a lunatic TV game show that caters openly to voyeurism, an eerie documentary explicating the medical and psychological problems of Siamese twins. DePalma's New York location work reveals facets of an over-familiar urban landscape untouched at the time by other filmmakers.

Most importantly, there is an appealing performance by Jennifer Salt as the investigative journalist who's cries of "Wolf!" go unheeded until it is almost too late, and Margot Kidder is touching and frightening as the most thoroughly bizarre heroine in movie history. Above all, however, "Sisters" revealed DePalma as capable of moving to the commercial center of the movie world without sacrificing the exuberantly radical spirit that first marked him as a director worth watching. "Sisters" provided moviegoers like myself with a special satisfaction of finding a real treasure while prowling cinema's bargain basement.